The invention relates to a piston pump, especially for supplying high-pressure fuel to a direct-injection internal combustion engine with a pump housing and a drive shaft for actuating one or several pump plungers that are oriented radially relative to the drive shaft in the pump housing, wherein the drive shaft is rotatably mounted on one or several bearings that extend between a shaft inlet opening of the pump housing and rear housing wall lying opposite the shaft inlet opening.
Such piston pumps are known in various constructions in the state of the art. For example, from DE 102 08 574 A1, a radial piston pump emerges that has a lifting ring arranged on an eccentric section of the drive shaft. The drive shaft is rotatably mounted in the pump housing a ball bearing arranged in the shaft inlet opening and in a sliding bearing in the region of the rear housing wall.
In US 2003/0145835 A1, a radial piston pump with a lifting ring arranged on an eccentric section of the drive shaft is also proposed, wherein the drive shaft is here mounted rotatably in the pump housing a needle bearing arranged in the region of the rear housing wall.
Another embodiment of a piston pump emerges from DE 198 27 926 A1. Instead of the lifting ring mounted eccentrically on the drive shaft, a multiple cam revolving with the drive shaft is provided for actuating a pump plunger and the drive shaft is mounted rotatably in the pump housing by using a ball bearing arranged on the rear housing wall.
One feature that is common to the embodiments of the piston pumps noted as examples is that each of the bearings arranged in the region of the rear housing wall requires an end journal of the drive shaft that attaches to the actual drive element in the form of the eccentrically mounted lifting ring or the cam. However, the axial installation space required by the journal can be critical with respect to the pump length, especially when the piston pump is used for supplying high-pressure fuel to a direct-injection internal combustion engine and is arranged in its cylinder head region. This is currently based on the fact that, in addition to the continuous goal of constructing the internal combustion engine as compact as possible and as space saving as possible, the free space required for satisfying heightened pedestrian regulations between the engine hood of a vehicle on one side and the internal combustion engine installed in the vehicle, including its add-on parts, on the other side must absolutely be maintained. For example, maintaining these regulations can become considerably more difficult under some circumstances if a longitudinal installation of the internal combustion engine in the vehicle is provided with a piston pump of conventional construction arranged in the extension of the cylinder head, wherein, due to its overall length, this piston pump penetrates into the prescribed free space underneath the engine hood of the vehicle.
As proposed in DE 196 50 246 A1, it would indeed be possible to shorten the overall length of the piston pump by eliminating the bearing in the region of the rear housing wall. However, such a floating support of the drive element is to be classified as fundamentally unfavorable with respect to its operating stability, and for sufficient stabilization requires further measures for supporting the drive shaft. Accordingly, the piston pump of this publication also involves a configuration without its own drive shaft that can be used in all cases in connection with a lengthened camshaft already supported with sufficient stability in the internal combustion engine.